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View Full Version : Simple Math



Saj
04-01-2003, 08:49 PM
Hi,

I am trying to create a javascript that says:

add a and b together and then divide it by 2.
(a + b) / 2

How would you do this?

Choopernickel
04-01-2003, 08:54 PM
function add(num1, num2) {
sum = num1 + num2;
return sum
}

function halve(num) {
half = num/2;
return half;
}

function sumAndHalve(numA, numB) {
numC = add(numA, numB);
numD = halve(numC);
return numD
}

then, anywhere, you'd call

sumAndHalve(3,1)

I know there are easier, more terse ways to code this, but I like to keep each operation separate. Is that so wrong?

Choopernickel
04-01-2003, 08:56 PM
I posted a new thread instead of posting a reply. D'oh! Check it.


<edit by="brothercake">
I merged your answer (above) into this thread
</edit>

beetle
04-01-2003, 09:12 PM
Or make some methods! I love methods!


Number.prototype.add = function()
{
var arg, i = 0, sum = this;
while( arg = arguments[i++] )
{
sum += parseInt( arg, 10 );
}
return sum;
}

Number.prototype.divide = function( denom )
{
return this / denom;
}

var a = 4;
var b = 2;

alert( a.add( b ).divide( 2 ) );

Choopernickel
04-01-2003, 09:16 PM
thanks, brothercake.

beetle, great solution. For some reason, I don't seem to consider extending the prototype until long after the original need is fulfilled by functions. Dur!

Saj
04-01-2003, 09:17 PM
ok thanks. would i be able to use variables already defined as the addends?

liorean
04-01-2003, 09:23 PM
Wouldn't this be cooler to have on an Array?
Array.prototype.sum=function(){
var
l=this.length,
r=0;
while(--l)
r+=this.[l];
return r;
}

Array.prototype.avg=function(){
var
k,
l=k=this.length,
r=0;
while(--l)
r+=this.[l];
return (r/k);
}

Then you can use [a,b].avg() for doing the job.

beetle
04-01-2003, 09:40 PM
Cooler? Yes? More practical? Your mileage may vary ;)

Choopernickel - extending the prototype is a large part of an upcoming article I'm writing for Sitepoint.com on javascript namespaces/scope :D It should be an eye-opener for many (I hope)

Choopernickel
04-01-2003, 09:56 PM
Excellent, beetle. I've gotten familiar with extending it through some string operations I've come up with, then with an Array.search() method that I think was pretty cool.

I'm SO freakin' happy to finallly have found a javascript forum where it's like, all serious javascripting and everything! :thumbsup: :o like you don't even know.

Saj
04-01-2003, 10:26 PM
Ok here's what I'm trying to do:



Number.prototype.add = function() {
var arg, i = 0, sum = this;
while( arg = arguments[i++] ) {
sum += parseInt( arg, 10 );
} return sum;
}

Number.prototype.divide = function( denom ) {
return this / denom;
}

function calculate() {
var a = document.triangle.a.value
var b = document.triangle.b.value
var c = document.triangle.c.value
var b2 = b*b
var c2 = c*c

if (a=" ") {
document.triangle.a.value = b2.add(c2).divide( 2 )
}
else {
javascript:calculate2()
}
}




For this one I want c - b, not c + b. I've spent ages on this, and can't firure it out.

Saj
04-01-2003, 10:30 PM
LOL Never Mind stupid question. I think I got it.

Saj
04-01-2003, 11:08 PM
Please tell me what I am doing wrong here!



function divide(num) {
half = num/2;
return half;
}

function calculate() {
var a = document.triangle.a.value;
var b = document.triangle.b.value;
var c = document.triangle.c.value;
var b2 = b*b;
var c2 = c*c;
var a2 = a*a;
var c2b2 = c2-b2;

if (a=" ") {
document.triangle.a.value = divide(c2b2);
}
else {
alert("Hello");
}
}


By the way, yes I am doing the pythagorean theorem. A few of the variables are not necessary now, but I need them later.

beetle
04-01-2003, 11:20 PM
All values retrieved from form elements are String-type variables. You need to convert them to Number-type with parseInt

var f = document.triangle;
var a = parseInt( f.a.value, 10 );
var b = parseInt( f.b.value, 10 );
var c = parseInt( f.c.value, 10 );

Which is why I suspect you also had problem using methods prototyped onto the Number object ;)

Saj
04-02-2003, 12:01 AM
Ok I see what your doing, but what is the need for the 10?

Saj
04-02-2003, 12:05 AM
Also, I'm still getting an answer of 4.5, when I want three, with this code:



function divide(num) {
half = num/2;
return half;
}

function calculate() {
var triangle = document.triangle;
var a = parseInt( triangle.a.value, 10 );
var b = parseInt( triangle.b.value, 10);
var c = parseInt( triangle.c.value, 10);
var a2 = a*a;
var b2 = b*b;
var c2 = c*c;
var c2b2 = c2-b2;

if (a=" ") {
document.triangle.a.value = divide(c2b2);
}
else {
alert("Hello");
}
}

cheesebagpipe
04-02-2003, 12:10 AM
hey beetle...

This works nicely with host arrays:

while (el = document.images[i++] )

...as they're nodelists, and must contain objects. A for loop is a better idea with user arrays (or passed arguments) - since any element that evaluates to false will break the loop.

<html>
<head>
<title>untitled</title>
</head>
<body>
<script type="text/javascript" language="javascript">

Number.prototype.add = function()
{
var arg, i = 0, sum = this;
while( arg = arguments[i++] )
{
sum += parseInt( arg, 10 );
}
return sum;
}

Number.prototype['add-o-rama'] = function()
{
for ( sum = this, i = 0; i < arguments.length; ++i ) sum += parseInt( arguments[i], 10 );
return sum;
}

x = 100;
y = x.add(0,999);
alert(y);

x = 100;
y = x['add-o-rama'](0,999);
alert(y);

</script>
</body>
</html>

The add-o-rama method is copyrighted. :p

beetle
04-02-2003, 12:46 AM
True, cheesebagpipe, but why would you want to add zero? :p

Saj,
There is no division in the pythagorean theorem, so I don't know why you are dividing.

a2 + b2 = c2

where c is the hypoteneuse. (those 2s are supposed to be superscript)

So, if you are trying to solve for a given [/B]b[/B] and [/B]c[/B], your math should be


a = Math.sqrt( c*c - b*b );

Or, you can use Math.pow() if you like


a = Math.sqrt( Math.pow( c, 2 ) - Math.pow( b, 2 ) );

Or, make your own Number methods


Number.prototype.sqrt = function()
{
return Math.sqrt( this );
}

Number.prototype.square = function()
{
return this.pow( 2 );
}

Number.prototype.pow = function( power )
{
return Math.pow( this, power );
}

a = ( c.square() - b.square() ).sqrt();

Saj
04-02-2003, 01:30 AM
You know, I am obviously going crazy. I dunno. Maybe just a long day of exams and stuff.

But thanks. I've never covered math in javascript. That helps. And yes I meant to get the square root, not divide by 2 :D Just proof of my insanity.

cheesebagpipe
04-02-2003, 01:41 AM
...why would you want to add zero? Beats me. Why would you want to pass anything but an integer? Might as well add a bit of input filtering, never hurts. Actually, I was speaking in a general sense, having fallen afoul of this a while back.

Interesting stuff here (http://www.merlyn.demon.co.uk/js-maths.htm)...not to me, I hate "maths"...:mad:

Saj
04-02-2003, 02:00 AM
One More question here:

How could you say:

If the value of the text box "a" is nothing, then do this. Otherwise, do this function.

I have this so far:



function calculate() {

if (a=" ") {
document.triangle.a.value = Math.sqrt(5*5 - 4*4);
}
else {
another_function();
}
}

cheesebagpipe
04-02-2003, 02:02 AM
if (a == "") {

beetle
04-02-2003, 02:11 AM
Originally posted by cheesebagpipe
Interesting stuff here (http://www.merlyn.demon.co.uk/js-maths.htm)...not to me, I hate "maths"...:mad: Ehh, some good ideas, but I don't like any of the implementation.

Saj
04-02-2003, 02:17 AM
No, that doesn't work. When I do that, nothing happens. Its just a non-working error.

The script works fine, but the only problem is that is I fill in the text box a, it does the it replaces it with the sum and square root of b and c, even if one isn't filled in.

cheesebagpipe
04-02-2003, 03:12 AM
Saj....it would probably be a good idea to pseudocode (http://www.minich.com/education/wyo/stylesheets/pseudocode.htm) this beforehand; it's a bit unclear from this thread exactly what you had in mind. Might want to check some of these (http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=javascript+pythagorean) out to see working approaches. :)

brothercake
04-02-2003, 10:45 AM
Originally posted by beetle
extending the prototype is a large part of an upcoming article I'm writing for Sitepoint.com on javascript namespaces/scope :D It should be an eye-opener for many (I hope)
Keep us informed on that :)

Saj
04-02-2003, 06:16 PM
Ok I think I have it now.

Just 2 things. What is the kill program command in js? Like in perl it's die. And, how do you say "if something does not equal this, this, and this, then do this?"

Thanks

beetle
04-02-2003, 06:25 PM
Well, the not-equal operator is != and the logical AND operator is &&. The logical OR operator is ||

There is no 'kill' command, but you can break out of a function using 'return' or kill a loop with 'break'.

liorean
04-02-2003, 06:38 PM
There's no analogue to kill program. Your best bet is return from within a function or break from within a block.

function(){
if(something!=somethingelse)return;
[...]
}


AnyValidIdentifier:{
[...]
if([boolean condition]){
break AnyValidIdentifier;
}
}

As for your conditional, you use the logic operators:
// ! (unary NOT)
if(!false)
statement;
// || (binary OR)
if(true||false)
statement;
else
statement;
// && (binary AND)
if(true&&false||true){
statements
}else if(1!=0){
statements
}else{
statements
}
or bitwise logic operators:

// & (binary AND)
if([number whatever] & [number bitMask])
statement;
// ^ (binary XOR)
if([number whatever] ^ [number bitMask])
statement;
// | (binary OR)
if([number whatever] | [number bitMask])
statement;
// ~ (unary NOT)
if(~[number whatever])
statement;
// Not very useful used like this - all it does is invert a number.

Saj
04-02-2003, 11:08 PM
Umm...Alright. I think I gotcha. That works well thanks :)



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